Why do I need to stat-grind ?
To kick The Fallen (140G) and the Absolute Conqueror (200G) in the nuts, and finish the 68 sidequests (200G) for a grand total of 540G. And, of course, to have a kick-ass party.
What is the best way to stat-grind ?
You would think you're supposed to link like crazy and fight everything you encounter to raise your BR as fast as possible, but it is the other way around. The idea here is to keep you BR very low so you can gain more stats between each BR. To do that, you have to follow a few rules :
Dodge EVERY ENEMY you see, and NEVER fight something that isn't a boss or a forced fight (like 2 immobile Skull Scavengers sitting on a chest, or Landworms in the mist). Save whenever you're not targeted and dodge like crazy getting all the chests (you will need what's inside for your über-characters).
Do every possible sidequest for cash and components (and because you have to), and finish ALL 42 sidequests of Disc 1 before leaving Nagapur to finish the disc. Try and do a shitload of Guild tasks for cash, new formations, achievements (at least one), and rare components you will need for your characters.
Last note : when you reach BR70 or so, you can disband all your unions and make a Rush-only union, and go grind in Robelia (room with the 10 Landworms) untill you build a chain of 500-1000, using only weapon and mystic arts commands. If you do that, you will gain only 2 or 3 BR and all your leaders (now in the roster) will have learned and improved all their arts. Great way to learn Second Chance and Kiss of Life and upgrade every art to its maximum level (or at least level IV).
Where should I grind on Disc 1 and on Disc 2 ?
1) When you hit BR10
, enter Blackdale regular entrance for a first boosting session, turn right and save before entering the Obsidian Trail. Go in and you will see a Skull Scavenger sleeping on the floor. Go and fight him. It is going to be hard, so if he kills one of your leaders or 2 or 3 of your soldiers, exit and retry. Stop when you're BR25. Before BR10-12, you will be too weak. Use 2 or 3 full unions.
Bring Glenys, Caedmon and Baulson to boost them. Try and get Emmy too to replace Emma. More on the soldiers at the end of this post.
You can use this boosting session to up Emma a bit and be able to kill Namul-Niram (her and Rush need to have Remedies to be able to beat the Remnant at a low BR). You can also stop this boosting session at BR18-20, do the Nest of Eagles quest, get Emmy ASAP, and finish grinding here with Emmy in your party untill BR25-30. Then finish all the sidequests of Disc1 (all 42 of them) and finish Disc1. You should be around BR38 when you start Disc2 with all quests finished.
2) When you reach BR40
at the beginning of Disc2, go in the Grammi Tier - Anatoray part of the Ancient Ruins, first room on the left (second floor, you need to beat Ymir to gain access). You will have 3 Rockgraters roaming free. Ice them, then go back to the teleporter in the first zone, save, reload, and kill them again untill you're BR60-65. Forget about the Charibdys in here for boosting. If you don't find the 3 Rockgraters and Grand Rockgraters where I tell you, just exit AR and re-enter untill you get the right set-up.
Upon entering the AR, you can find on the first floor : Charibdys, Rockgraters, or nothing. Try each set-up, each one leading to different monsters in the next floors. Just try untill you get the monsters you need. This is also true for finding the Ancbolders on the third floor (they can be replaced by Greater Demons, in which case you will also find the Brynhildrs you need for one achieve).
3) When you reach BR60-65
, grind in the Metopon Tier - Boreas (third floor). Go there after killing Holy Servant to get the key (he's in the room in front of the teleporter on the second floor) and kill Ancbolders, the giants I already talked about. They're easy and give a shitload of stats. Then do the save and reload trick in the room that leads to Demi-God.
To get the Jewel Steel you will need for almost every character's ultimate weapons, use the monster set-up that makes a single Diatryma appear in front of you when you reach the second floor. Save on the first floor, fight the Diatryma, and do the save/reload trick untill he drops Jewel Steel. He drops it 1/3 of the time, and by the numbers of 2 or 3, so he's the best and fastest way the get the precious metal in the game.
Let me be clear on this : apart from the DLC bosses, there isn't a single enemy that will give you better stats than Ancbolders, so when you reach BR90-100 and your stats don't upgrade much anymore, continue, you have no better choice. Also, when you get Hawkarang (the first weapon art you will get with Glenys's Swordflash), you can go kill The Fallen, then come back and grind some more.
Last thing : don't worry about following all this to the letter. When you feel like progressing the story, or do sidequests, or hike for components for Rush or your leaders, do it. It doesn't matter, really. Just do 1 big grinding session with Caedmon, Baulson and Emmy on Disc1 (with Glenys in the roster, or you can even use her), and 2 big ones on Disc2 in AR, the first versus Rockgraters untill you can pwn Holy Servant, then against Ancbolders untill you're god-like. This is the general idea.
Opening Ancient Ruins ?
Talk to the big Yama on the right of Athlum's pub, at the end of the street, and he will put a new Siebenbur Path on your map (the 2nd one). Go in, travel to the upper-left dead-end and open the Ancient Ruins with your beautiful DLC key (the DLC is free). You should be around BR40 when you enter this place. You can find Ancient Ruins maps on GameFAQs. They help a lot since you don't have your radar on in here.
Who should I use ?
Last but not least, you should use who you like, of course, but IMO Torgal, Baulson, Emmy, Jager, Caedmon and Glenys are the best. Irina is a very good healer and Psionics user, but you need muscle, not mystics, and all the people I have named are awsome healers too, except Torgal and Jager. You could also like Dave and Blocter, even Pagus, but I wouldn't use them. At the end of the game, Dave is useless, and Blocter has no weapon art even if he becomes immune to all satus-effects. The best choice of the 3 would be Pagus who has healing abilities and 2 weapon arts (one unique), but you can do better than him since he doesn't hurt much, and you will need hurt. Lots of it.
The only rule is to recruit the leaders you want ASAP, before grinding, put them in your active party, and NEVER change them. That's what I did with Baulson, Caedmon and Jager/Glenys. Once they're on the team, they stay on the team, because if you change a lot, they won't be as strong as they could.
What about the soldiers ?
On my third playtrough, I changed things and liked it. A lot. So here it is for you :
Union 1 : Rush, Baulson, Combat soldier, Herbs soldier, Herbs soldier.
Union 2 : Torgal, Glenys, Combat soldier, Herbs soldier, Herbs soldier.
Union 3 : Emmy, Caedmon, Combat soldier, Herbs soldier, Herbs soldier.
Rush, Baulson, Caedmon, Emmy and Glenys will be healing tanks at the end of the game, each one having Kiss of Life and Second Chance, so you don't need weaker units using Recovery arts. Forget about Lotions. And when I say "Combat soldier", I mean a soldier that uses, and I stress this, only weapon arts, has a 2-handed weapon, and a dual-wield combat style. For example, a soldier who holds a Tabar-Zin (like Blocter) with 2 hands, or a huge katana with 2 hands. These soldiers are the ones who have the more HP and do the more damage.
This set-up is for big fights. You can use 4 unions when grinding. This will allow you to boost 3 more soldiers. I would select the 3 Recovery arts users that have the most HP, and include them in the boosting sessions, you never know. Always select the soldiers that have the most HP. When you reach your last roster upgrade (before the 6 bases I think), check if a soldier or 2 are better than the ones you're using. If so, switch to them, and never switch again.
What about gear ?
Your soldiers can end the game with Divine weapons, so you can grind untill they upgrade to these. Also, they will must likely have a Roseraphim Bracelet for their HP. When you get your Goddess Wristlet, Emmy should ask for it. Give it to her, and some BR after that, everybody will clone it, giving you a +50% HP boost. I had to wait untill BR130, so be patient.
Finally, always say "Yes" when a leader asks for something (the most important being giving Emmy her Nightbloom), and always respond "Combat arts, of course" when a leader asks for advice. One false answer and Torgal will end with a gay magic wand instead of Halphas Dominus and Hawkarang. Also, at the end of the game, look for the Snievan's Belt print (defeat Enlightened Seven I think). Make it with the right components. Some leader will ask for it. Say "Yes" and most characters will clone it as well. It is the best attack accessory in the game, save for the Black Belt which is nearly impossible to make.
What about formations ?
I have found a good set of formations for the usual tanks (Rush, Jager, Emmy, Torgal, Baulson and Caedmon) which results in 4 unions 4-5-5-4 with Gobelet III Arrow II Arrow II Gobelet III. It's very balanced HP and ATK wise so your 4 unions are the same (no weak link). Adapt when using only 2 or 3 unions, of course, but I would stick with Gobelet III and Arrow II.
Finally, here are 2 other things I wrote to help a little…
FAQ on DLC bosses and how to defeat them
FAQ on auto-upgrading weapons and equipment